1. Technical Field
The present invention generally relates to digital video distribution and more particularly to testing digital video distribution environments for pixel errors.
2. Background Art
A digital video distribution environment is a common installation in residences and commercial buildings. Increasingly, more sophisticated and expansive digital video distribution environments are employed to distribute digital video. There is now a demand for an improved system and method for testing such digital video distribution environments.
Prior art FIG. 1 is a block diagram of an illustrative digital video distribution environment 10. The digital video distribution environment 10 links four (4) digital video sources 11A-D, such as a Blu-ray player, with eight (8) digital video sinks 15A-H, such as a television. Between the four digital video sources 11A-D and eight digital video sinks 15A-H are processing components, such as encoders and decoders. Each path from a source to a sink including all intermediary processing components is a distribution path 16. For example, the distribution path 16 between the first digital video source 11A and the first digital video sink 15A includes the first processing component 12 and the second processing component 13.
Digital video streams comprise a plurality of pixels organized into a plurality of frames. The number of pixels per frame corresponds to the resolution of the digital video. For example, one frame of video at a resolution of 1080p (i.e. 1920 horizontal pixels×1080 vertical pixels), a common resolution, comprises 2,073,600 pixels. At a frame rate of 60 frames per second (fps), ten seconds of digital video at a resolution of 1080p comprises 1,244,160,000 pixels.
Each pixel further comprises color coordinates, which define the color of the pixel. For example, in the red green blue (RGB) color coordinate system, each pixel comprises a red color coordinate, a green color coordinate and a blue color coordinate. A full red pixel in the RGB color coordinate system with 8 bit color depth comprises a red color coordinate of 255, a green color coordinate of zero, and a blue color coordinate of zero.
As the complexity of digital video distribution environments 10 increases, video issues become increasingly more difficult to diagnose and correct. Various factors including intermediary processing and interference may cause visible errors in the displayed video. These visible errors can adversely affect a user's viewing experience and must be diagnosed and corrected. One malfunctioning component of a digital video distribution environment 10 can cause video issues with the entire digital video distribution environment 10, potentially causing consumer dissatisfaction with the other fully functional components.
More specifically, pixel errors are known to those skilled in the art as a factor related to less than optimal viewing experience. A pixel error is a pixel that has one or more color coordinates altered during transmission from the digital video source 11A-D to the digital video sink 15A-H, resulting in discolored pixels displayed by the digital video sink. Pixel errors commonly occur when distributing compressed or encoded digital video or digital video processed with other lossy methods.
Methods and systems for testing a digital video distribution environment 10 are known in the prior art. However, due to the precise nature of digital video there is currently a trend toward automated diagnosis of video issues. Increasingly, diagnostic data is processed to achieve an objective score or result, taking human analysis and subjective criteria out of the equation. In instances where an objective score is not computed, the diagnostic results are often provided as a set of data values. This is undesirable, as the methodology for objective scores can be opaque and diagnostic data can be difficult to interpret or understand.
Visually displaying pixel errors provides a technician with a diagnostic tool for use in the field. The technician may make quick diagnoses of display issues by recognizing common patterns of pixel errors. Additionally, with a visual display of pixel errors, the installer may more intuitively relate the diagnoses to untrained clients. Methods and systems for visually diagnosing pixel errors are known in the prior art. More specifically, methods and systems are known for generating a differential video including pixels computed from the mathematical differences between a reference video bit stream before and after processing. Accordingly, pixel errors in the differential video are displayed according to their magnitude and at their native resolution.
Refer to prior art FIG. 2. As an example of the above prior art method assume a pixel 211 of the reference video bit stream 21 has a red color coordinate of two hundred forty (240), a green color coordinate of one hundred (100) and a blue color coordinate of one hundred (100) before processing. Next, assume that after passing through the distribution path 16, the pixel 221 has a red color coordinate of two hundred (200), a green color coordinate of one hundred fifty (150), and a blue color coordinate of one hundred fifty (150) after processing. According to known methods, a differential pixel is displayed having color coordinates that are the differences between the pixel color values before and after processing. Accordingly, a differential video would be displayed having a corresponding pixel with red, green and blue coordinates of fifty (50), forty (40), and forty (40), respectively.
Those skilled in the art will recognize that this method is suitable for locating pixel errors of a large magnitude or large contiguous clusters of pixel errors. However, pixels errors of a small magnitude may be visually indistinguishable from pixels without errors. Similarly, individual pixels or small clusters of pixels are difficult to detect. Consequently, there is a need for a system and method of testing digital video to emphasize the location of pixel errors.